This invention relates to a process for skinning or peeling produce, such as tomatoes and peaches and similar fruits, in which the layer of the produce directly under its skin is quickly heated by steam. The invention is also directed to an apparatus for performing the method.
German Patent Publication (Offenlegungsschrift) No. 2,060,447 discloses a process for peeling tomatoes in which the tomatoes are fed to a steamer. Steam is discharged from jets into the steamer at a temperature of about 360.degree. to 400.degree. C and at a pressure of up to 3 atmospheres, whereby the skins of the tomatoes are rapidly heated, so that the water directly under the skin of the tomatoes is brought to a boil. This boiling tears the skins, so that a part of the skin falls off the body of the tomatoes. As described in said publication, the known method has the disadvantage that only a part of the skin falls off. Hence manual completion of the peeling of the tomatoes is necessary following the steam treatment in order to remove the remainder of the skin. In addition, the steam acts in a nonuniform manner on the tomatoes, so that the tomatoes are partly overheated and partly underheated. Besides, this process requires the use of equipment to superheat the steam and having sufficient capacity. The cost of such equipment is rather high.
This publication also discloses a process in which the tomatoes are heated to a temperature of about 60.degree. to 100.degree. C and then put into a vacuum of less than 300 mm of Mercury. Consequently, the skins explosively burst open due to the rapid boiling of the liquid under the skin. This process has the disadvantage that it requires the use of vacuum equipment. In addition, in said further known method the treatment of the surface area of the tomatoes is also not uniform and it is also necessary following the vacuum treatment to manually handle at least those tomatoes to which skin still partially adheres in order to completely remove the skins.
It is also known to remove the skins from potatoes or similar hard produce by means of a steam peeler, as described in German Pat. No. 1,234,690 and in U.S. Pat. No. 3,164,181. In the process described in these publications, the pressure within a pressure vessel containing the potatoes is brought to a pressure of about 7 atmospheres (gauge) within about 10 seconds. The potatoes are exposed to this pressure for about 45 seconds while rotating the pressure vessel. The pressure is then released and the potatoes are removed from the pressure vessel. The process is limited, however, for peeling only relatively hard produce, such as potatoes.
The above mentioned German Pat. No. 1,234,690 discloses a peeling apparatus which includes a pressure vessel with a hydraulically operated device for opening and closing the vessel. A source of pressure is provided to operate the hydraulic arrangement. A pressure cylinder is mounted inside the pressure vessel. A piston in the cylinder is connected through a piston rod to a cover to open and close the pressure vessel from within. The cover is held in the open position by means of a spring. The pressure vessel, the hydraulically operated opening and closing device and the cover are supported for rotation as a unit. The pressure cylinder is connected to said pressure source by means of a connecting conduit. The pressure cylinder is provided with discharge openings in its cylinder wall. These openings are arranged so that the pressure outlets are uncovered by the piston only when the cover is closed.
The spring employed in this arrangement is subject to a substantial tension, and is hence subject to a very large wear and tear. In addition, the cover is not completely opened as soon as the spring force slackens. In addition, the arrangement has the disadvantage that the cover may be closed by switching on of the pressure in any position of the system. Therefore, the operator must continually pay attention that the pressure is not accidentally switched on when tending the pressure vessel, for example, for refilling.